Coherent and spectral beam combining of fiber lasers using volume Bragg gratings

Five-channel spectral beam combining (SBC) using volume Bragg gratings (VBGs) in photo-thermo-refractive (PTR) glass with 0.5 nm spectral separation between channels and combined power >750 W has been recently reported. We report on improvements in this technique with the use of thermal control of VBGs that allows precise high-power alignment required for dense SBC with 0.25 nm spectral separation of channels. Experimental results of passive coherent beam combining (CBC) of fiber lasers using multiplexed VBGs are presented and analyzed. Methods for achieving 100 kW class systems using novel hybrid architectures that combine both coherent and spectral beam combining are discussed.